W. E. Rose disclosed two Roots type intermeshing impellers for fluid handling apparatus of the rotary positive displacement type in his U.S. Pat. No. 3,089,638. In reviewing his FIG. 1 a lobe portion 34 of the right rotor 26 intermeshing a waist portion 32 of the left rotor 25 with a large contacting area rather than a single-point contact as recited in his specification. Such a larger contacting area when the two rotors are intermeshed and intersected at a right angle between the two rotors, a great friction loss will be caused to reduce its overall output energy. The specific rotor profile of Rose prior art is formed with a deeply recessed waist area 32, thereby producing an abrupt "deflection point" such as designated as numeral 25a, 26a as shown in FIG. 7 (accompanying with thi application) which may influence a smooth rotatable engagement between the two rotors 25, 26.
When the two rotors of Rose prior art are rotatated at 45 degrees from its ordinate or abscissa, the abrupt "deflection points" 25a, 26a of the two rotors are not smoothly engageable with each other, still possibly causing wearing of their interfaces or even vibrational shock during the running. If Rose rotors are inferentially modified to have too shallow concave waist portions 32 as shown in dotted line of FIG. 7, they are smoothly engageable, but still having a larger contacting area for causing friction loss.
Brun's U.S. Pat. No. 3,056,355 has also such an abrupt deflection point "P" between the waist portion and the outer lobe portion. So, a clearance between the rotor and the casing is provided for the smooth running of his rotors, entailing considerable loss of output due to such clearance.
Hubrich did not specify the relationship between a curvature radius of the waist recess portion and another curvature radius of the lobe portion in his U.S. Pat. No. 3,105,634. However, in view of his FIGS. 6 and 4, his waist curvature radius is about 1.3-1.6 times larger than the lobe radius. It means that the curvature radius of the rotor waist portion is still too small to provide a shallow concave waist portion so that a deeply recessed waist portion of one rotor may increase its contacting area with the other rotor when rotatably intermeshed at a right angle therebetween, thereby causing a greater friction loss and reducing its output.
The present inventor has found the drawbacks of the rotor profiles of conventional Roots type rotary fluid machines and invented the present rotary fluid machine having smoothly operating rotors.